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Dec 20, 2013 1300 UTC Day 1 Convective Outlook

December 20, 2013

Dec 20, 2013 1300 UTC Day 1 Convective Outlook

day1otlk

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0657 AM CST FRI DEC 20 2013

VALID 201300Z – 211200Z

…THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF S CNTRL TX NEWD THROUGH THE ARKLATEX…

…SYNOPSIS…
AN AMPLIFIED…PROGRESSIVE SPLIT-FLOW PATTERN WILL PREVAIL OVER THE LWR 48 THIS PERIOD…DOWNSTREAM FROM BROAD RIDGE IN THE E PACIFIC. POTENT NRN BAJA CA UPR LOW WILL TRACK E ACROSS NW MEXICO TODAY BEFORE TURNING SLIGHTLY N OF E INTO SE NM AND FAR W TX EARLY SAT AS RIDGE HOLDS FIRM OVER THE WRN ATLANTIC/ERN GULF OF MEXICO. A SHORTWAVE IMPULSE ROTATING AROUND THE BAJA LOW…MARKED BY VORT MAX NOW APPROACHING THE BAJA SPUR…WILL SERVE TO FURTHER AMPLIFY THE LARGER-SCALE LOW/TROUGH THROUGH THE PERIOD.

AT LWR LVLS…SHALLOW ARCTIC INTRUSION NOW IN PROGRESS OVER THE SRN PLNS…IN CONJUNCTION WITH THE EWD ADVANCE OF THE BAJA SYSTEM…WILL RESULT IN A STRONG S CNTRL TX-TO-LWR OH VLY FRONTAL ZONE BY THE END OF THE PERIOD. THIS BAROCLINIC ZONE…AND INCREASINGLY WARM/MOIST AIR SPREADING NWD TO ITS EAST…WILL SET THE STAGE FOR INCREASING TSTM COVERAGE LATER TODAY AND…ESPECIALLY…TNGT/SAT OVER A BROAD SWATH EXTENDING FROM PARTS OF NM AND TX NEWD INTO OH AND KY. SOME OF THE STORMS COULD BECOME SVR EARLY SAT OVER PARTS TX AND THE ARKLATEX.

…CNTRL TX/ARKLATEX LATER IN PERIOD…
SFC…VWP…AND SATELLITE OBSERVATIONS SUGGEST THAT SUBSTANTIAL MOISTURE WILL CONTINUE TO STREAM N AND NNE ACROSS SRN AND ERN TX AND THE LWR MS VLY THROUGH TNGT…IN STRENGTHENING LOW-LVL FLOW AHEAD OF AFOREMENTIONED COLD FRONT. SFC DEWPOINTS IN THE MID 60S F SHOULD BECOME ESTABLISHED FROM CNTRL TX E/NE INTO THE LWR MS VLY.

BEYOND LOW-LVL WAA AND FRONTAL UPLIFT…HOWEVER…FORCING FOR ASCENT ACROSS THIS REGION WILL REMAIN WEAK THROUGH EARLY TNGT. COUPLED WITH EXISTING WARM NOSE IN THE 850-700 LAYER AND ABUNDANT CLOUD COVER…TSTM COVERAGE THROUGH THE DAY SHOULD REMAIN LIMITED.

LATER TNGT AND…ESPECIALLY…EARLY SAT…APPRECIABLE /ON THE ORDER OF 60 M/ HEIGHT FALLS WILL BEGIN TO OVER SPREAD S CNTRL TX AS THE BAJA SYSTEM APPROACHES THE REGION. COUPLED WITH AN ASSOCIATED STRENGTHENING OF SSWLY 850 MB FLOW /SPEEDS INCREASING TO AOA 65 KTS/ AND PERSISTENT MOISTENING…SETUP SHOULD SUPPORT A FAIRLY WIDESPREAD BLOSSOMING OF SHOWERS AND TSTMS ALONG AND N OF THE FRONT FROM WRN AND S CNTRL TX NEWD THROUGH THE ARKLATEX INTO SE MO/SRN IL.

MOST OF THE ELEVATED ACTIVITY SHOULD REMAIN NON-SVR…ALTHOUGH SUFFICIENT ELEVATED BUOYANCY MAY ARISE FOR MARGINALLY SVR HAIL IN S CNTRL TX. OF GREATER SVR CONCERN…HOWEVER…WILL BE THE CONDITIONAL RISK FOR SFC OR NEAR SFC-BASED STORMS ALONG THE IMMEDIATE FRONT…OR PERHAPS JUST AHEAD OF IT…LATER TNGT AND EARLY SAT FROM S CNTRL TX NE TO THE ARKLATEX.

GIVEN THE STRENGTH OF THE LLJ…700 MB FLOW INCREASING TO AOA 60 KTS…LIKELY PROGRESSION OF UPR TROUGH…AND SFC DEWPOINTS APPROACHING 70F OVER WRN PARTS OF THE TX CSTL PLN…SETUP MAY YIELD A CONDITIONAL RISK FOR SUPERCELL/LEWP CIRCULATIONS CAPABLE OF DMGG WIND AND/OR TORNADOES. THIS THREAT WOULD BE GREATEST AFTER 09Z…AND LIKELY WILL PERSIST/SPREAD FARTHER E/NE BEYOND 12Z SAT.

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